THE (KA=0-]1) SUBMILLIMETER ROTATION-TUNNELING SPECTRUM OF THE WATER DIMER

The (Ka=0→1) submillimeter rotation-tunneling transitions of the water dimer have been observed. The (H2O)2 clusters were produced in a slit nozzle arrangement and the transitions were detected by direct absorption of the submillimeter radiation. A number of lines in the allowed subbranches (Ka=0, E±→Ka=1, E∓), (Ka=0, A1-→Ka=1, A1+) and (Ka=0, A1+→Ka=1, A1-1) have been studied. Combination differences using microwave transitions within the (Ka=0) and (Ka=1) states allowed an unambiguous assignment of the lines. The present results allow a more accurate determination of the A-rotational constant and the tunneling splittings of (Ka=0) and (Ka=1). Further they show that the K-type doubling constant has a different sign for the lower and upper tunneling states in (Ka=1). © 1990.